Grease composition

ABSTRACT

A grease composition comprising a lubricating base oil combined with (A) 2-30 wt % of a thickener and 
 
(B) 0.1-10 wt % of at least one type of compound selected from the group consisting of phosphorus compounds represented by general formulas (1) and (2) below and their metal salts or amine salts, based on the total weight of the composition.  
                 
          [wherein X 1 , X 2  and X 3  each represent an oxygen atom or sulfur atom, with at least two from among X 1 , X 2  and X 3  being oxygen atoms, and R 1 , R 2  and R 3  each represent hydrogen or a C1-30 hydrocarbon group] 
                 
    [wherein X 4 , X 5 , X 6  and X 7  each represent an oxygen atom or sulfur atom, with at least three from among X 4 , X 5 , X 6  and X 7  being oxygen atoms, and R 4 , R 5  and R 6  each represent hydrogen or a C1-30 hydrocarbon group].

TECHNICAL FIELD

The present invention relates to a grease composition.

BACKGROUND ART

Grease is commonly used as a lubricant for mechanical parts such asconstant velocity gears, transmission gears, ball bearings, rollerbearings and the like.

Most of the members composing such mechanical parts are made of metal,and friction between the metal members generates heat and wear at thesections of contact, resulting in a shorter life of the grease or of themechanical parts themselves. Therefore, various additives such asfriction reducers are included in lubricants to reduce the frictionbetween metals.

In recent years, however, the higher performance and lighter weights ofsuch mechanical parts have resulted in restrictions on the conditionsfor their use, and friction due to contact between the metals occursmore frequently. With these types of mechanical parts, it is often notpossible to achieve an adequate friction-reducing effect even when usingconventional greases containing added friction reducers.

In addition, grease-filled mechanical parts are more frequently beingused at ever higher temperatures, and therefore a grease which canprovide a high friction-reducing effect even at high temperatures hasbeen strongly desired.

The present invention has been accomplished in light of thesecircumstances of the prior art, and its object is to provide a greasecomposition which can exhibit a high friction-reducing effect even athigh temperatures.

In order to achieve this object, the grease composition of the inventionis characterized by comprising a lubricating base oil combined with (A)2-30 wt % of a thickener and (B) 0.1-10 wt % of at least one type ofcompound selected from the group consisting of phosphorus compoundsrepresented by general formulas (1) and (2) below and their metal saltsor amine salts, based on the total weight of the composition.

[wherein X¹, X² and X³ may be the same or different and each representsan oxygen atom or sulfur atom, with at least two from among X¹, X² andX³ being oxygen atoms, and R¹, R² and R³ may be the same or differentand each represents hydrogen or a C1-30 hydrocarbon group]

[wherein X⁴, X⁵, X⁶ and X⁷ may be the same or different and eachrepresents an oxygen atom or sulfur atom, with at least three from amongX⁴, X⁵, X⁶ and X⁷ being oxygen atoms, and R⁴, R⁵ and R⁶ may be the sameor different and each represents hydrogen or a C1-30 hydrocarbon group].

According to the invention, combining a lubricating base oil with (A) athickener and (B) at least one type of compound selected from the groupconsisting of phosphorus compounds represented by general formulas (1)and (2) above and their metal salts or amine salts in prescribed amountsyields a grease composition having a sufficiently high friction-reducingeffect, and maintaining the high friction-reducing effect even at hightemperature. Thus, even with increased speeds and lighter weights ofmechanical parts such as constant velocity gears, or the use of suchmechanical parts at high temperatures, it is possible to prevent heatgeneration and wear due to friction between metals, to achievesatisfactorily lengthening of the usable life of grease and mechanicalparts.

The grease composition of the invention preferably further comprises anorganic molybdenum compound.

The (A) thickener in the grease composition of the invention ispreferably lithium soap.

Alternatively, the (A) thickener in the grease composition of theinvention is preferably a urea-based thickener, and more preferably aurea-based thickener represented by the following general formula (3).A-CONH—R⁷—NHCO—B  (3)[wherein A and B may be the same or different and each is a grouprepresented by —NHR⁸, —NR⁹R¹⁰ or —OR¹¹ (where R⁸, R⁹, R¹⁰ and R¹¹ may bethe same or different and each represents a C6-20 hydrocarbon group),and R⁷ is a divalent hydrocarbon group].

The grease composition of the invention preferably comprises at leastone compound selected from among compounds represented by generalformula (1) wherein X¹, X² and X³ are all oxygen atoms and compoundsrepresented by general formula (2) wherein X⁴, X⁵, X⁶ and X⁷ are alloxygen atoms. In this case, component (B) may include both a compoundwherein X¹—X⁷ are all oxygen atoms and a compound wherein one from amongX¹—X⁷ is a sulfur atom while the others are oxygen atoms, but component(B) is preferably composed of only a compound wherein X¹—X⁷ are alloxygen atoms.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1A and 1B are a perspective view and top view, respectively, of atest strip used for a friction test.

BEST MODE FOR CARRYING OUT THE INVENTION

Preferred embodiments of the present invention will now be explained indetail.

As lubricating base oils to be used in the grease composition of theinvention there may be mentioned mineral oils and/or synthetic oils.

Mineral oils include, for example, those obtained by methods commonlyemployed in lubricating oil production processes for petroleum refining,and more specifically, there may be mentioned oils obtained by ordinarypressure distillation or reduced pressure distillation of crude oil,followed by purification of the lubricating oil fraction by oildeasphalting, solvent extraction, hydrogenating decomposition, solventdewaxing, catalytic dewaxing, hydrogenation refining, sulfuric acidwashing, clay refining and the like.

As specific examples of synthetic oils there may be mentioned polyα-olefins such as polybutene, 1-octene oligomer and 1-decene oligomer ortheir hydrogenated forms; diesters such as ditridecyl glutarate,di-2-ethylhexyl adipate, diisodecyl adipate, ditridecyl adipate anddi-3-ethylhexyl sebacate; polyol esters such as trimethylolpropanecaprylate, trimethylolpropane pelargonate, pentaerythritol2-ethylhexanoate and pentaerythritol pelargonate; alkylnaphthalenes;alkylbenzenes; polyoxyalkylene glycols; polyphenyl ethers;dialkyldiphenyl ethers; silicone oils; and mixtures thereof.

The dynamic viscosity of these lubricating base oils at 100° C. ispreferably 2-40 mm²/s and more preferably 3-20 mm²/s. The viscosityindex of the base oil used is preferably 90 or greater and morepreferably 100 or greater.

According to the invention, the aforementioned lubricating base oil iscombined with (A) a thickener and (B) at least one type of compoundselected from the group consisting of phosphorus compounds representedby general formulas (1) and (2) above and their metal salts or aminesalts in prescribed amounts. Hereunder, these components will sometimesbe referred to as component (A) and component (B).

There are no particular restrictions on the (A) thickener, butsoap-based thickeners, for example, are preferably used. Using asoap-based thickener can increase the effect of preventing damage tomechanical parts.

As specific examples of soap-based thickeners there may be mentionedsodium soaps, calcium soaps, aluminum soaps and lithium soaps, butlithium soaps are preferred among these from the standpoint of moistureresistance and thermal stability. As examples of lithium soaps there maybe mentioned lithium stearate and lithium-12-hydroxystearate.

Preferred examples for the (A) thickener are urea-based thickeners.Using a urea-based thickener can increase the effect of preventingdamage to mechanical parts.

As examples of urea-based thickeners there may be mentioned ureacompounds such as diurea compounds, triurea compounds, tetraureacompounds and polyurea compounds (other than diurea compounds, triureacompounds and tetraurea compounds), urethane compounds such asurea-urethane compounds and diurethane compounds, and mixtures thereof.Preferred among these are diurea compounds, urea-urethane compounds,diurethane compounds and mixtures thereof.

Preferred examples of urea-based thickeners are those represented by thefollowing general formula (3).A-CONH—R⁷—NHCO—B  (3)

The compounds represented by general formula (3) include diureacompounds, urea-urethane compounds and diurethane compounds.

In formula (3), A and B may be the same or different and each is a grouprepresented by —NHR⁸, —NR⁹R¹⁰ or —OR¹¹. Here, R⁸, R⁹, R¹⁰ and R¹¹ may bethe same or different and each represents a C6-20 hydrocarbon group.

As examples of hydrocarbon groups represented by R⁸, R⁹, R¹⁰ and R¹¹there may be mentioned straight-chain or branched alkyl, straight-chainor branched alkenyl, cycloalkyl, alkylcycloalkyl, aryl, alkylaryl andarylalkyl. More specifically there may be mentioned straight-chain orbranched alkyl groups such as hexyl, heptyl, octyl, nonyl, decyl,undecyl, dodecyl, tridecyl, tetradecyl, pentadecyl, hexadecyl,heptadecyl, octadecyl, nonadecyl and eicosyl; straight-chain or branchedalkenyl groups such as hexenyl, heptenyl, octenyl, nonenyl, decenyl,undecenyl, dodecenyl, tetradecenyl, pentadecenyl, hexadecenyl,heptadecenyl, octadecenyl, nonadecenyl and eicosenyl; cyclohexyl groups;alkylcyclohexyl groups such as methylcyclohexyl, dimethylcyclohexyl,ethylcyclohexyl, diethylcyclohexyl, propylcyclohexyl,isopropylcyclohexyl, 1-methyl-3-propylcyclohexyl, butylcyclohexyl,amylcyclohexyl, amylmethylcyclohexyl, hexylcyclohexyl, heptylcyclohexyl,octylcyclohexyl, nonylcyclohexyl, decylcyclohexyl, undecylcyclohexyl,dodecylcyclohexyl, tridecylcyclohexyl and tetradecylcyclohexyl; arylgroups such as phenyl and naphthyl; alkylaryl groups such as toluyl,ethylphenyl, xylyl, propylphenyl, cumenyl, methylnaphthyl,ethylnaphthyl, dimethylnaphthyl and propylnaphthyl; and arylalkyl groupssuch as benzyl, methylbenzyl and ethylbenzyl, among which cyclohexyl,octadecyl and toluyl groups are particularly preferred.

R⁷ in formula (3) is a divalent hydrocarbon group. As specific divalenthydrocarbon groups there may be mentioned straight-chain or branchedalkylene groups and straight-chain or branched alkenylene,cycloalkylene, arylene, alkylarylene and arylalkylene groups. The numberof carbon atoms of the divalent hydrocarbon group represented by R⁷ ispreferably 6-20 and more preferably 6-15.

As preferred examples of divalent hydrocarbon groups represented by R⁷there may be mentioned ethylene, 2,2-dimethyl-4-methylhexylene andgroups represented by the following formulas (4) to (13), among whichgroups represented by formulas (5) and (7) are preferred.

The compounds represented by formula (3) may be obtained, for example,by reacting a diisocyanate represented by OCN—R⁷—NCO with a compoundrepresented by R⁸NH₂, R⁹R¹⁰NH or R¹¹OH or a mixture thereof in the baseoil at 10-200° C. R⁷, R⁸, R⁹, R¹⁰ and R¹¹ in the formulas for the rawmaterial compounds have the same respective definitions as R⁷, R⁸, R⁹,R¹⁰ and R¹¹ in formula (3)

Bentone, silica gel or the like may be used as the (A) thickener.

The content of component (A) in the grease composition of the inventionis 2-30 wt % based on the total weight of the composition. If thecontent of the thickener is less than 2 wt %, the effect of adding thethickener will be insufficient, producing a less than satisfactorygrease condition of the grease composition. For the same reason, thecontent of component (A) is preferably at least 5 wt % and morepreferably at least 10 wt % based on the total composition. If thecontent of component (A) is greater than 30 wt %, the grease compositionwill become too hard and will fail to exhibit sufficient lubricatingperformance. For the same reason, the thickener content is preferably nogreater than 25 wt % and more preferably no greater than 20 wt % basedon the total composition.

Component (B) of the grease composition of the invention is at least onetype of compound selected from the group consisting of phosphoruscompounds represented by general formulas (1) and (2) below and theirmetal salts or amine salts.

[wherein X¹, X² and X³ may be the same or different and each representsan oxygen atom or sulfur atom, with at least two from among X¹, X² andX³ being oxygen atoms, and R¹, R² and R³ may be the same or differentand each represents hydrogen or a C1-30 hydrocarbon group]

[wherein X⁴, X⁵, X⁶ and X⁷ may be the same or different and eachrepresents an oxygen atom or sulfur atom, with at least three from amongX⁴, X⁵, X⁶ and X⁷ being oxygen atoms, and R⁴, R⁵ and R⁶ may be the sameor different and each represents hydrogen or a C1-30 hydrocarbon group].

As specific C1-30 hydrocarbon groups represented by R¹ to R⁶ there maybe mentioned alkyl, cycloalkyl, alkenyl, alkylcycloalkyl, aryl,alkylaryl and arylalkyl.

As examples of the aforementioned alkyl groups there may be mentionedalkyl groups such as methyl, ethyl, propyl, butyl, pentyl, hexyl,heptyl, octyl, nonyl, decyl, undecyl, dodecyl, tridecyl, tetradecyl,pentadecyl, hexadecyl, heptadecyl and octadecyl (which alkyl groups maybe either straight-chain or branched).

As examples of the aforementioned cycloalkyl groups there may bementioned C5-7 cycloalkyl groups such as cyclopentyl, cyclohexyl andcycloheptyl. As examples of the aforementioned alkylcycloalkyl groupsthere may be mentioned C6-11 alkylcycloalkyl groups such asmethylcyclopentyl, dimethylcyclopentyl, methylethylcyclopentyl,diethylcyclopentyl, methylcyclohexyl, dimethylcyclohexyl,methylethylcyclohexyl, diethylcyclohexyl, methylcycloheptyl,dimethylcycloheptyl, methylethylcycloheptyl and diethylcycloheptyl (withany desired position of substitution of the alkyl groups on thecycloalkyl groups).

As examples of the aforementioned alkenyl groups there may be mentionedalkenyl groups such as butenyl, pentenyl, hexenyl, heptenyl, octenyl,nonenyl, decenyl, undecenyl, dodecenyl, tridecenyl, tetradecenyl,pentadecenyl, hexadecenyl, heptadecenyl and octadecenyl (which alkenylgroups may be either straight-chain or branched, and the double bond maybe at any desired position).

As examples of the aforementioned aryl groups there may be mentionedaryl groups such as phenyl and naphthyl. As examples of theaforementioned alkylaryl groups there may be mentioned C7-18 alkylarylgroups such as tolyl, xylyl, ethylphenyl, propylphenyl, butylphenyl,pentylphenyl, hexylphenyl, heptylphenyl, octylphenyl, nonylphenyl,decylphenyl, undecylphenyl and dodecylphenyl (which alkyl groups may beeither straight-chain or branched, with any desired position ofsubstitution on the aryl groups).

As examples of the aforementioned arylalkyl groups there may bementioned C7-12 arylalkyl groups such as benzyl, phenylethyl,phenylpropyl, phenylbutyl, phenylpentyl and phenylhexyl (wherein thealkyl groups may be either straight-chain or branched).

The C1-30 hydrocarbon groups represented by R¹ to R⁶ are preferablyC1-30 alkyl groups or C6-24 aryl groups, more preferably C3-18 alkylgroups, and even more preferably C4-12 alkyl groups.

R¹, R² and R³ may be the same or different and each represents hydrogenor one of the aforementioned hydrocarbon groups, with preferably 1 to 3,more preferably 1-2 and even more preferably 2 from among R¹, R² and R³being the aforementioned hydrocarbon groups.

Also, R⁴, R⁵ and R⁶ may be the same or different and each representshydrogen or one of the aforementioned hydrocarbon groups, withpreferably 1 to 3, more preferably 1 or 2 and even more preferably 2from among R⁴, R⁵ and R⁶ being the aforementioned hydrocarbon groups.

In the phosphorus compounds represented by general formula (1), at leasttwo from among X¹ to X³ must be oxygen atoms, but preferably all of X¹to X³ are oxygen atoms.

In the phosphorus compounds represented by general formula (2), at leastthree from among X⁴ to X⁷ must be oxygen atoms, but preferably all of X⁴to X⁷ are oxygen atoms.

As examples of phosphorus compounds represented by general formula (1)there may be mentioned phosphorous acid and monothiophosphorous acid;phosphorous acid monoesters and monothiophosphorous acid monoestershaving one of the aforementioned C1-30 hydrocarbon groups; phosphorousacid diesters and monothiophosphorous acid diesters having two of theaforementioned C1-30 hydrocarbon groups; phosphorous acid triesters andmonothiophosphorous acid triesters having three of the aforementionedC1-30 hydrocarbon groups; and mixtures thereof. Preferred among theseare phosphorous acid monoesters and phosphorous acid diesters, withphosphorous acid diesters being more preferred.

As examples of phosphorus compounds represented by general formula (2)there may be mentioned phosphoric acid and monothiophosphoric acid;phosphoric acid monoesters and monothiophosphoric acid monoesters havingone of the aforementioned C1-30 hydrocarbon groups; phosphoric aciddiesters and monothiophosphoric acid diesters having two of theaforementioned C1-30 hydrocarbon groups; phosphoric acid triesters andmonothiophosphoric acid triesters having three of the aforementionedC1-30 hydrocarbon groups; and mixtures thereof. Preferred among theseare phosphoric acid monoesters and phosphoric acid diesters, withphosphoric acid diesters being more preferred.

As salts of the phosphorus compounds represented by general formula (1)and (2) there may be mentioned salts having all or a portion of theacidic hydrogens of the phosphorus compound neutralized. Such phosphoruscompound salts may be obtained by reacting phosphorus compounds withmetal bases such as metal oxides, metal hydroxides, metal carbonates andmetal chlorides, or nitrogen compounds such as ammonia or aminecompounds having only C1-30 hydrocarbon groups or hydroxylgroup-containing hydrocarbon groups in the molecule.

As metals for these metal bases there may be mentioned, specifically,alkali metals such as lithium, sodium, potassium and cesium, alkalineearth metals such as calcium, magnesium and barium, and heavy metalssuch as zinc, copper, iron, lead, nickel, silver and manganese.Preferred among these are alkaline earth metals such as calcium andmagnesium, and zinc.

The aforementioned phosphorus compound metal salts differ in structuredepending on the valence of the metals and the numbers of OH groups orSH groups in the phosphorus compounds, and therefore no restrictions areplaced on the structure. For example, when 1 mole of zinc oxide isreacted with 2 moles of a phosphoric acid diester (one OH group), acompound having the structure represented by formula (14) below may beobtained as the major product, although it may also be obtained as apolymerized molecule.

As another example, 1 mole of zinc oxide may be reacted with 1 mole of aphosphoric monoester (two OH groups) to obtain a compound having thestructure represented by formula (15) below as the major product,although it may also be obtained as a polymerized molecule.

As examples of the aforementioned nitrogen compounds there may bementioned ammonia, monoamines, diamines, polyamines and the like.Specific examples include alkylamines with C1-30 alkyl groups such asmethylamine, ethylamine, propylamine, butylamine, pentylamine,hexylamine, heptylamine, octylamine, nonylamine, decylamine,undecylamine, dodecylamine, tridecylamine, tetradecylamine,pentadecylamine, hexadecylamine, heptadecylamine, octadecylamine,dimethylamine, diethylamine, dipropylamine, dibutylamine, dipentylamine,dihexylamine, diheptylamine, dioctylamine, dinonylamine, didecylamine,diundecylamine, didodecylamine, ditridecylamine, ditetradecylamine,dipentadecylamine, dihexadecylamine, diheptadecylamine,dioctadecylamine, methylethylamine, methylpropylamine, methylbutylamine,ethylpropylamine, ethylbutylamine and propylbutylamine (wherein thealkyl groups may be either straight-chain or branched);

alkenylamines with C2-30 alkenyl groups such as ethenylamine,propenylamine, butenylamine, octenylamine and oleylamine (wherein thealkenyl groups may be either straight-chain or branched); alkanolamineshaving C1-30 alkanol groups such as methanolamine, ethanolamine,propanolamine, butanolamine, pentanolamine, hexanolamine, heptanolamine,octanolamine, nonanolamine, methanolethanolamine, methanolpropanolamine,methanolbutanolamine, ethanolpropanolamine, ethanolbutanolamine andpropanolbutanolamine (wherein the alkanol groups may be eitherstraight-chain or branched);

alkylenediamines having C1-30 alkylene groups such as methylenediamine,ethylenediamine, propylenediamine and butylenediamine; polyamines suchas diethylenetriamine, triethylenetetramine, tetraethylenepentamine andpentaethylenehexamine; compounds having C8-20 alkyl groups or alkenylgroups on the aforementioned monoamines, diamines or polyamines, such asundecyldiethylamine, undecyldiethanolamine, dodecyldipropanolamine,oleyldiethanolamine, oleylpropylenediamine andstearyltetraethylenepentamine, or heterocyclic compounds such asN-hydroxyethyloleylimidazoline; alkylene oxide adducts of thesecompounds; and mixtures thereof.

Preferred among these nitrogen compounds are aliphatic amines (eitherstraight-chain or branched) having C10-20 alkyl groups or alkenylgroups, such as decylamines, dodecylamines, tridecylamines,heptadecylamines, octadecylamines, oleylamines and stearylamines.

According to the invention, component (B) is preferably a metal salt oramine salt of a phosphorus compound represented by general formula (1)or (2) above, and it is more preferably a metal salt of the phosphoruscompound. Using such compounds as component (B) will tend to produce agreater friction-reducing effect.

From the standpoint of thermal stability there are preferred phosphoruscompounds represented by general formula (2) and their salts.

The compounds for component (B) may be used alone or in combinations oftwo or more.

The content of component (B) is 0.1-10 wt % based on the totalcomposition. If the content of component (B) is less than 0.1 wt %, thefriction-reducing effect will be insufficient, and reduction of frictionbetween metal members of mechanical parts will be impossible to achieveespecially at high temperature. For the same reason, the content ofcomponent (B) is preferably 0.3 wt % or greater and more preferably 0.5wt % or greater based on the total composition. If the content ofcomponent (B) exceeds 10 wt %, no commensurate improvement in thefriction-reducing effect will be achieved. For the same reason, thecontent of component (B) is preferably no greater than 7 wt % and morepreferably no greater than 5 wt % based on the total composition.

The grease composition of the invention comprises component (A) andcomponent (B) described above added to the lubricating base oil, but itmay also contain an organic molybdenum compound in addition to thesecomponents.

As examples of organic molybdenum compounds to be used for the inventionthere may be mentioned the phosphoric acid or thiophosphoric acid esterderivatives represented by general formula (16) below, and thedithiocarbamic acid ester derivatives represented by general formula(17) below.

In general formulas (16) and (17), each R may be the same or differentand represents a C1 or greater hydrocarbon group, the c number of Xgroups may be the same or different with each representing an oxygen orsulfur atom, and a, b and c each represent integers of 1-6.

As examples of hydrocarbon groups represented by R in formulas (16) and(17) above there may be mentioned C1-24 alkyl groups, C5-7 cycloalkylgroups, C6-11 alkylcycloalkyl groups, C6-18 aryl groups, C7-24 alkylarylgroups and C7-12 arylalkyl groups.

As the aforementioned alkyl groups there may be mentioned, specifically,methyl, ethyl, propyl (including all branched isomers), butyl (includingall branched isomers), pentyl (including all branched isomers), hexyl(including all branched isomers), heptyl (including all branchedisomers), octyl (including all branched isomers), nonyl (including allbranched isomers), decyl (including all branched isomers), undecyl(including all branched isomers), dodecyl (including all branchedisomers), tridecyl (including all branched isomers), tetradecyl(including all branched isomers), pentadecyl (including all branchedisomers), hexadecyl (including all branched isomers), heptadecyl(including all branched isomers), octadecyl (including all branchedisomers), nonadecyl (including all branched isomers), eicosyl (includingall branched isomers), heneicosyl (including all branched isomers),docosyl (including all branched isomers), tricosyl (including allbranched isomers) and tetracosyl (including all branched isomers).

As the aforementioned cycloalkyl groups there may be mentioned,specifically, cyclopentyl, cyclohexyl and cycloheptyl.

As the aforementioned alkylcycloalkyl groups there may be mentioned,specifically, methylcyclopentyl (including all substitution isomers),ethylcyclopentyl (including all substitution isomers),dimethylcyclopentyl (including all substitution isomers),propylcyclopentyl (including all branched isomers, substitutionisomers), methylethylcyclopentyl (including all substitution isomers),trimethylcyclopentyl (including all substitution isomers),butylcyclopentyl (including all branched isomers, substitution isomers),methylpropylcyclopentyl (including all branched isomers, substitutionisomers), diethylcyclopentyl (including all substitution isomers),dimethylethylcyclopentyl (including all substitution isomers),methylcyclohexyl (including all substitution isomers), ethylcyclohexyl(including all substitution isomers), dimethylcyclohexyl (including allsubstitution isomers), propylcyclohexyl (including all branched isomers,substitution isomers), methylethylcyclohexyl (including all substitutionisomers), trimethylcyclohexyl (including all substitution isomers),butylcyclohexyl (including all branched isomers, substitution isomers),methylpropylcyclohexyl (including all branched isomers, substitutionisomers), diethylcyclohexyl (including all substitution isomers),dimethylethylcyclohexyl (including all substitution isomers),methylcycloheptyl (including all substitution isomers), ethylcycloheptyl(including all substitution isomers), dimethylcycloheptyl (including allsubstitution isomers), propylcycloheptyl (including all branchedisomers, substitution isomers), methylethylcycloheptyl (including allsubstitution isomers), trimethylcycloheptyl (including all substitutionisomers), butylcycloheptyl (including all branched isomers, substitutionisomers), methylpropylcycloheptyl (including all branched isomers,substitution isomers), diethylcycloheptyl (including all substitutionisomers) and dimethylethylcycloheptyl (including all substitutionisomers).

As the aforementioned aryl groups there may be mentioned, specifically,phenyl and naphthyl.

As the aforementioned alkylaryl groups there may be mentioned,specifically, tolyl (including all substitution isomers), xylyl(including all substitution isomers), ethylphenyl (including allsubstitution isomers), propylphenyl (including all branched isomers,substitution isomers), methylethylphenyl (including all substitutionisomers), trimethylphenyl (including all substitution isomers),butylphenyl (including all branched isomers, substitution isomers),methylpropylphenyl (including all branched isomers, substitutionisomers), diethylphenyl (including all substitution isomers),dimethylethylphenyl (including all substitution isomers), pentylphenyl(including all branched isomers, substitution isomers), hexylphenyl(including all branched isomers, substitution isomers), heptylphenyl(including all branched isomers, substitution isomers), octylphenyl(including all branched isomers, substitution isomers), nonylphenyl(including all branched isomers, substitution isomers), decylphenyl(including all branched isomers, substitution isomers), undecylphenyl(including all branched isomers, substitution isomers), dodecylphenyl(including all branched isomers, substitution isomers), tridecylphenyl(including all branched isomers, substitution isomers), tetradecylphenyl(including all branched isomers, substitution isomers), pentadecylphenyl(including all branched isomers, substitution isomers), hexadecylphenyl(including all branched isomers, substitution isomers), heptadecylphenyl(including all branched isomers, substitution isomers) andoctadecylphenyl (including all branched isomers, substitution isomers).

As examples of the aforementioned arylalkyl groups there may bementioned benzyl, phenethyl, phenylpropyl (including all branchedisomers) and phenylbutyl (including all branched isomers).

As compounds represented by general formula (16) and (17) there may bementioned, specifically, molybdenum phosphate, molybdenum thiophosphate,molybdenum dithiophosphate and molybdenum dithiocarbamate.

The phosphoric acid or thiophosphoric acid ester derivatives representedby general formula (16) above and the dithiocarbamic acid esterderivatives represented by general formula (17) above are usuallycompounds obtained by reacting phosphoric acid esters, thiophosphoricacid esters or dithiocarbamic acid esters with inorganic molybdenumcompounds (molybdenum trioxide, molbdenic acid or its salts, etc.), andif necessary together with a sulfur source.

Molybdenum can take different valence states, and therefore thecompounds obtained by the aforementioned reaction will usually bemixtures. The most typical compounds are those represented by thefollowing formulas (18) and (19).

According to the invention, the organic molybdenum compound used may beany one of the compounds represented by general formulas (16) and (17)above, or a mixture thereof, but from the standpoint of thermalstability it is preferably a compound represented by general formula(16). Addition of a compound represented by general formula (16) canprovide excellent thermal stability particularly when the greasecomposition of the invention is used as bearing grease.

The proportion of the organic molybdenum compound added is preferably atleast 0.1 wt % and more preferably at least 0.5 wt % based on the totalcomposition. If the proportion is less than 0.1 wt %, the addition ofthe organic molybdenum compound will tend to yield no furtherfriction-reducing effect. The proportion of the organic molybdenumcompound added is also preferably no greater than 20 wt % and morepreferably no greater than 10 wt % based on the total composition. Ifthe proportion is greater than 20 wt %, there will tend to be nocommensurate improvement in the friction-reducing effect.

The grease composition of the invention may also contain, if necessary,solid lubricants, extreme pressure agents, antioxidants, oil agents,rust inhibitors, viscosity index improvers and the like to furtherenhance the performance, in a range which does not impair theproperties.

As specific solid lubricants there may be mentioned graphite, graphitefluoride, polytetrafluoroethylene, molybdenum disulfide, antimonysulfide, alkali (alkaline earth) metal borates and the like.

As specific extreme pressure agents there may be mentioned organic zinccompounds such as zinc dialkyldithiophosphates, zincdiaryldithiophosphates, zinc dialkyldithiocarbamates and zincdiaryldithiocarbamates, and sulfur-containing compounds such asdihydrocarbyl polysulfide, sulfidized esters, thiazole compounds andthiadiazole compounds.

As specific antioxidants there may be mentioned phenol-based compoundssuch as 2,6-di-t-butylphenol and 2,6-di-t-butyl-p-cresol; amine-basedcompounds such as dialkyldiphenylamines, phenyl-α-naphthylamine andp-alkylphenyl-α-naphthylamines; sulfur-based compounds; andphenothiazine-based compounds.

As specific oil agents there may be mentioned amines such aslaurylamine, dimyristylamine, palmitylamine, stearylamine andoleylamine; higher alcohols such as lauryl alcohol, myristyl alcohol,palmityl alcohol, stearyl alcohol and oleyl alcohol; higher fatty acidssuch as lauric acid, myristic acid, palmitic acid, stearic acid andoleic acid; fatty acid esters such as methyl laurate, methyl myristate,methyl palmitate, methyl palmitate, methyl stearate and methyl oleate;amides such as lauryl amide, myristyl amide, palmityl amide, stearylamide and oleyl amide; fats and oils, and the like.

As specific rust inhibitors there may be mentioned metal soaps;polyhydric alcohol partial esters such as sorbitan fatty acid esters;amines; phosphoric acid; phosphoric acid salts, and the like.

As specific viscosity index improvers there may be mentionedpolymethacrylates, polyisobutylene, polystyrene, and the like.

The grease composition of the invention may be obtained, for example, byadding component (A), component (B) and an organic molybdenum compoundor other additives to a lubricating base oil, stirring the mixture, andpassing it through a roll mill or the like. The grease composition ofthe invention may also be obtained by preadding the raw material ofcomponent (A) to the lubricating base oil and melting the mixture,stirring and mixing it to prepare component (A) in the lubricating baseoil, and then further adding component (B) and an organic molybdenumcompound or other additives, stirring the mixture and passing it througha roll mill or the like.

The grease composition of the invention having the composition describedabove exhibits a sufficiently high friction-reducing effect, and thefriction-reducing effect is maintained at a high level at hightemperature. It is therefore highly useful as a gear grease for constantvelocity gears and transmission gears, as a bearing grease for ballbearings and roller bearings, and as an iron-manufacturing plant grease,and is particularly preferred as a grease for constant velocity joints,non-stage transmission bearings, and both automotive and railroadbearings.

EXAMPLES

The present invention will now be explained in greater detail throughexamples and comparative examples, with the understanding that theseexamples are in no way limitative on the invention.

Examples 1-12, Comparative Examples 1-24

Grease compositions were prepared according to the procedure describedbelow, using a poly-α-olefin (dynamic viscosity at 40° C.: 48 mm²/s) inExamples 1-3, Comparative Examples 1-3 and Comparative Examples 13-15,and a mineral oil (dynamic viscosity at 40° C.: 100 mm²/s) in Examples4-12, Comparative Examples 4-12 and Comparative Examples 16-24, as thelubricating base oil.

In Examples 1-9, Comparative Examples 1-9 and Comparative Examples13-21, diphenylmethane 4,4′-diisocyanate (MDI) was added to thelubricating base oil and heated to prepare a solution whilecyclohexylamine or additionally stearyl alcohol was added to thelubricating base oil and heated to prepare a solution, and the twosolutions were combined so that the MDI, cyclohexylamine and stearylalcohol were in the molar ratios shown in Tables 1-4. The additiveslisted below were then added to the produced gel-like substance in thecontents shown in Tables 1-4, and the mixture was stirred and passedthrough a roll mill to obtain the desired grease composition.

In Examples 10-12, Comparative Examples 10-12 and Comparative Examples22-24, lithium 12-hydroxystearate was added to the lubricating base oiland heated to prepare a solution, and after cooling, the additiveslisted below were added in the contents shown in Tables 2-4. The mixturewas then stirred and passed through a roll mill to obtain the desiredgrease composition.

Additives

ZnP: Zinc di(n-butyl)phosphate (phosphorus content: 13.2 wt %, sulfurcontent: 0%, zinc content: 13.0 wt %)

MODTC: Molybdenum dioctyldithiocarbamate

MoDTP: Molybdenum dioctyldithiophosphate

ZnDTP: Zinc dipentyldithiophosphate

[Friction Test]

The grease compositions of Examples 1-12 and Comparative Examples 1-24were used for a friction test in the following manner.

FIGS. 1A and 1B are a perspective view and top view, respectively, of atest strip used for the friction test. As shown in these drawings, 1 gof the grease composition was filled into a needle holder 2 (14 mm×10mm×2.5 mm) formed at the center of a lower disk 1 (φ24 mm×7.9 mm), andthen three needles (φ3 mm×13.8 mm) were placed in the needle holder 2and an upper disk 4 (φ20 mm×13 mm) was situated thereover. Each of thetest strips was set in an SRV friction testing machine in such a manneras to form an angle θ [deg] (the needle set angle) of 30 deg betweenline 1 ₁ perpendicular to the sliding direction of the upper disk 4through the center O on the upper surface of the lower disk 1 and line 1₂ parallel to the lengthwise direction of the needle 3 through thecenter O. The two temperature conditions 80° C. and 150° C. were used inthe testing machine, and the friction test was carried out at afrequency of 40 Hz, an amplitude of 3 mm and a load of 1000 N. Thefriction coefficients at 10 minutes after start of the test are shown inTables 1-4. TABLE 1 Example 1 Example 2 Example 3 Example 4 Example 5Example 6 Example 7 Example 8 Example 9 Thickener Raw MDI 1 1 1 1 1 1 55 5 material Cyclohexylamine 2 2 2 2 2 2 8 8 8 ratio Stearyl alcohol — —— — — — 2 2 2 [mol] Lithium 12-hydroxystearate — — — — — — — — — Content[wt %] 15 15 15 15 15 15 8 8 8 Base oil Mineral oil [wt %] — — — 83 8181 90 88 88 PAO [wt %] 83 81 81 — — — — — Additives ZnP [wt %] 2 2 2 2 22 2 2 2 MoDTC [wt %] — 2 — — 2 — — 2 — MoDTP [wt %] — — 2 — — 2 — — 2Friction Friction 80° C. 0.055 0.045 0.040 0.055 0.045 0.040 0.055 0.0450.040 test coefficient 150° C. 0.055 0.045 0.045 0.055 0.045 0.045 0.0550.045 0.045

TABLE 2 Example Example Example Comp. Comp. Comp. Comp. Comp. Comp. 1011 12 Ex. 1 Ex. 2 Ex. 3 Ex. 4 Ex. 5 Ex. 6 Thickener Raw MDI — — — 1 1 11 1 1 material Cyclohexylamine — — — 2 2 2 2 2 2 ratio Stearyl alcohol —— — — — — — — — [mol] Lithium 12-hydroxystearate used used used — — — —— — Content [wt %] 10 10 10 15 15 15 15 15 15 Base oil Mineral oil [wt%] 88 86 86 — — — 85 83 83 PAO [wt %] — — — 85 83 83 — — — Additives ZnP[wt %] 2 2 2 — — — — — — MoDTC [wt %] — 2 — — 2 — — 2 — MoDTP [wt %] — —2 — — 2 — — 2 Friction Friction 80° C. 0.055 0.045 0.040 0.180 0.0500.055 0.190 0.050 0.055 test coefficient 150° C. 0.055 0.045 0.045 0.2300.120 0.160 0.230 0.120 0.160

TABLE 3 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 7 Ex.8 Ex. 9 Ex. 10 Ex. 11 Ex. 12 Ex. 13 Ex. 14 Ex. 15 Thickener Raw MDI 5 55 — — — 1 1 1 material Cyclohexylamine 8 8 8 — — — 2 2 2 ratio Stearylalcohol 2 2 2 — — — — — — [mol] Lithium 12-hydroxystearate — — — usedused used — — — Content [wt %] 8 8 8 10 10 10 15 15 15 Base oil Mineraloil [wt %] 92 90 90 90 88 88 — — — PAO [wt %] — — — — — — 83 81 81Additives ZnP [wt %] — — — — — — — — — MoDTC [wt %] — 2 — — 2 — — 2 —MoDTP [wt %] — — 2 — — 2 — — 2 ZnDTP [wt %] — — — — — — 2 2 2 FrictionFriction 80° C. 0.185 0.050 0.055 0.180 0.055 0.055 0.050 0.045 0.040test coefficient 150° C. 0.235 0.130 0.165 0.225 0.125 0.230 0.195 0.0900.130

TABLE 4 Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Comp. Ex. 16 Ex.17 Ex. 18 Ex. 19 Ex. 20 Ex. 21 Ex. 22 Ex. 23 Ex. 24 Thickener Raw MDI 11 1 5 5 5 — — — material Cyclohexylamine 2 2 2 8 8 8 — — — ratio Stearylalcohol — — — 2 2 2 — — — [mol] Lithium 12-hydroxystearate — — — — — —used used used Content [wt %] 15 15 15 8 8 8 10 10 10 Base oil Mineraloil [wt %] 83 81 81 90 88 88 88 86 86 PAO [wt %] — — — — — — — — —Additives ZnP [wt %] — — — — — — — — — MoDTC [wt %] — 2 — — 2 — — 2 —MoDTP [wt %] — — 2 — — 2 — — 2 ZnDTP [wt %] 2 2 2 2 2 2 2 2 2 FrictionFriction 80° C. 0.050 0.045 0.040 0.050 0.045 0.040 0.050 0.045 0.040test coefficient 150° C 0.190 0.085 0.130 0.185 0.090 0.135 0.190 0.0850.135

Tables 1 and 2 show that when the grease compositions of Examples 1-12were used, a high friction-reducing effect was achieved as indicated bysufficiently low friction coefficients under both temperature conditionsof 80° C. and 150° C. When the grease compositions of Examples 2, 3, 5,6, 8, 9, 11 and 12 were used, which further contained an organicmolybdenum compound, it was possible to further increase thefriction-reducing effect.

When the grease compositions of Comparative Examples 1-24 were used,however, the friction coefficient was low especially at 150° C., andtherefore the friction property was inadequate at high temperature.

INDUSTRIAL APPLICABILITY

As explained above, the present invention provides a grease compositionexhibiting a sufficiently high friction-reducing effect, and thefriction-reducing effect is maintained at a high level at hightemperature. Thus, even with increased speeds and lighter weights ofmechanical parts such as constant velocity gears, or the use of suchmechanical parts at high temperatures, it is possible to prevent heatgeneration and wear due to friction between metals, to achievesatisfactorily lengthening of the usable life of the grease andmechanical parts.

1. A grease composition comprising a lubricating base oil combined with(A) 2-30 wt % of a thickener and (B) 0.1-10 wt % of at least one type ofcompound selected from the group consisting of phosphorus compoundsrepresented by general formulas (1) and (2) below and their metal saltsor amine salts, based on the total weight of the composition.

 [wherein X¹, X² and X³ may be the same or different and each representsan oxygen atom or sulfur atom, with at least two from among X¹, X² andX³ being oxygen atoms, and R¹, R² and R³ may be the same or differentand each represents hydrogen or a C1-30 hydrocarbon group]

 [wherein X⁴, X⁵, X⁶ and X⁷ may be the same or different and eachrepresents an oxygen atom or sulfur atom, with at least three from amongX⁴, X⁵, X⁶ and X⁷ being oxygen atoms, and R⁴, R⁵ and R⁶ may be the sameor different and each represents hydrogen or a C1-30 hydrocarbon group].2. A grease composition according to claim 1, which further comprises anorganic molybdenum compound.
 3. A grease composition according to claim1, wherein said thickener is a lithium soap.
 4. A grease compositionaccording to claim 1, wherein said thickener is a urea-based thickener.5. A grease composition according to claim 1, wherein said thickener isa urea-based thickener represented by the following general formula (3).A-CONH—R⁷—NHCO—B (3) [wherein A and B may be the same or different andeach is a group represented by —NHR⁸, —NR⁹R¹⁰ or —OR¹¹ (where R⁸, R⁹,R¹⁰ and R¹¹ may be the same or different and each represents a C6-20hydrocarbon group), and R⁷ is a divalent hydrocarbon group].
 6. A greasecomposition according to claim 1, which comprises at least one compoundselected from among compounds represented by general formula (1) whereinX¹, X² and X³ are all oxygen atoms and compounds represented by generalformula (2) wherein X⁴, X⁵, X⁶ and X⁷ are all oxygen atoms.